InfiniBand™ (IB) is a switched-fabric communications architecture primarily used in high-performance computing. It has been standardized by the InfiniBand Trade Association. Computing devices (host processors and peripherals) connect to the IB fabric via a network interface controller (NIC), which is referred to in IB parlance as a channel adapter. Host processors (or hosts) use a host channel adapter (HCA), while peripheral devices use a target channel adapter (TCA). IB defines both a layered hardware protocol (physical, link, network, and transport layers) and a software layer, which manages initialization and communication between devices. The transport layer is responsible for in-order packet delivery, partitioning, channel multiplexing and transport services, as well as data segmentation when sending and reassembly when receiving.
InfiniBand specifies the following transport services:                Reliable Connection (RC). RC provides reliable transfer of data between two entities, referred to as a requester and a responder. As a connection-oriented transport, RC requires a dedicated queue pair (QP) for each pair of requester and responder processes.        Unreliable Connection (UC). UC permits transfer of data between two entities. Unlike RC, UC but does not guarantee message delivery or ordering. Each pair of connected processes requires a dedicated UC QP.        Reliable Datagram (RD). Using RD enables a QP to send and receive messages from one or more QPs using a reliable datagram channel (RDC) between each pair of reliable datagram domains (RDDs). RD provides most of the features of RC, but does not require a dedicated QP for each process.        Unreliable Datagram (UD). With UD, a QP can send and receive messages to and from one or more remote QPs, but the messages may get lost, and there is no guarantee of ordering or reliability. UD is connectionless, allowing a single QP to communicate with any other peer QP.        Raw Datagram. A raw datagram is a data link layer service, which provides a QP with the ability to send and receive raw datagram messages that are not interpreted.        
A recent enhancement to InfiniBand is the Extended Reliable Connected (XRC) transport service (as described, for instance, in “Supplement to InfiniBand™ Architecture Specification Volume 1.2.1, Annex A14: Extended Reliable Connected (XRC) Transport Service”, 2009, Revision 1.0). XRC enables a shared receive queue (SRQ) to be shared among multiple processes running on a given host. As a result, each process can maintain a single send QP to each host rather than to each remote process. A receive QP is established per remote send QP and can be shared among all the processes on the host.
U.S. Patent Application Publication 2011/0116512, whose disclosure is incorporated herein by reference, describes a dynamically-connected (DC) transport service, in which a single DC initiator context is allocated for serving multiple requests from an initiator process running on an initiator host to transmit respective data to multiple target processes running on one or more target nodes. A first connect packet referencing the DC initiator context is directed to a first target process so as to open a first dynamic connection with the first target process, followed by transmission of first data. The first dynamic connection is closed after the transmission of the first data, and a second connect packet is transmitted so as to open a second dynamic connection with a second target process, followed by transmission of second data.